There has been a recognized need for ground penetrating radars (GPR) to locate, map, identify and image underground objects. Numerous applications for ground penetrating radars exist in both civilian and military applications. Civilian applications include road surface assessment, underground utility mapping, geophysical exploration, environmental surveys, road and bridge surface evaluation, archaeological exploration, and building wall (or other structural element) internal investigation. Military applications include land mine detection, explosive ordnance disposal, and underground bunker location; there are many other applications. Some of these applications are served by human portable ground-based system, some by vehicle carried mobile ground-based systems, and others by airborne systems.
The potential benefits of GPR has spurred numerous design and systems approaches. Initially these were centered on continuous wave system approaches including frequency modulated continuous wave (FMCW) and pulsed frequency modulated (PFM) approaches. Physical size limits the number of antennas, so the array gain is low, resulting in inadequate resolution and low penetration into the ground. The systems are wideband, which limits the coherent processing of an underground return. As a result, target imaging, detectability, and false alarm capabilities are below those desired.
Current ground based portable GPRs generally require that the antennas be in contact with the ground. This limits applicability to suitable terrain, and the requirement to reposition the antennas is very time consuming.
Airborne Side Looking radars are known utilizing synthetic aperture beam processing, resulting in excellent two-dimensional resolution; however this approach is not suitable for ground penetrating radar, where a three-dimensional image is required.
More recently, impulse radar (also known as ultrawideband radar) has been used in ground penetrating radar. Impulse radars and various applications for them are well known; see e.g. U.S. Pat. Nos. 5,361,070 to McEwan; 5,589,838 to McEwan; 5,523,760 to McEwan; and 5,517,198 to McEwan, all incorporated herein by reference. Impulse radars utilize the time, rather than the frequency domain, transmitting a single pulse rather than a train of sinusoidal signals, and have advantages over frequency based radar systems. The pulse width (duration) can be varied to match target size and depth characteristics. Impulse radar lends itself to digital rather than analog processing. Current GPR designs using this approach have several disadvantages, however. Systems that utilize large antenna arrays to achieve the desired resolution require a large number of antenna elements and the required electronic beam steering system is very complicated. Systems that scan each element of the three-dimensional search space require extreme amounts of data to be processed, resulting in severe processing requirements.
A need exists for a radar for penetrating ground or other material (e.g. water, building walls, etc.) that has improved resolution and depth capability and which can provide three dimensional imaging capability. There is a need for such a radar for portable, mobile, and airborne applications. Applications range from detecting small objects near the surface of the ground (or other material) to those that detect large objects buried deeply.